The cRc recommends Kellogg's cereals with only a k on the box. In my experience, I have not heard of anybody who disagrees with this. This is an unusual situation, though, since normally a plain
k does not indicate reliable kashrut supervision. According to a Kellogg's official representative, cereals with the K hechsher are under the supervision of the Rabbinical Council of New England.
My question is as follows: since the box does not include a copyright-protected kosher symbol, if the Rabbinical Council of New England were to withdraw their certification, Kellogg's would legally be able to continue to print the K on the boxes. How would the kosher consumer know that the product is no longer certified reliably?